It appears we're on the cusp of a major breakthrough in the prevention of HIV/AIDS. The FDA said yesterday that Truvada, a drug currently used to treat patients with HIV, appears to be effective at preventing HIV infection in healthy people. This would be the first drug of its kind and would obviously have a huge impact on the efforts to stop the spread of the deadly virus.

Tomorrow, a panel of FDA advisers is set to review Truvada, which is made by Gilead Sciences, and vote on whether it should be approved as a preventative treatment for HIV. While the FDA doesn't have to follow the panel's recommendation, it commonly does. If approved, the pill would then be allowed to be marketed to and prescribed for those patients who had a high risk of contracting HIV through sexual intercourse.

A three-year-long study on Truvada found that "daily doses cut the risk of infection in healthy gay and bisexual men by 44 percent, when accompanied by condoms and counseling." A second study found that it cut infection by 75 percent in heterosexual couples where one of the partners was healthy and the other had HIV. While it certainly holds a great deal of promise, some researchers warn that this pill is not the same as using a condom, which remains the most powerful weapon against HIV.

There is also concern because the drug has not been as effective in preventing infection in women. It's not clear whether the problem is that women require a higher dose or whether the women in the study in question were not taking the pills daily as prescribed. That's an issue that definitely needs to be sorted out, but if the drug is approved it's likely to be embraced quickly, since there's really nothing else like it in the pipeline and an AIDS vaccine is probably many years from being a reality.